It's the day when Ed Miliband presses the pause button on his conference programme to show whether he could be the next Prime Minister and lead a Labour government.
It's because it's the day when he lets his Shadow Chancellor do all the talking.
Spending up to £4 billion on a new housebuilding programme and stamp duty holiday for first time buyers is classic stimulus spending - using government funds to kick start a section of the economy.
In this case, construction.
The argument Mr Balls made on the stage of the conference hall today was the same one he's been making since he took the job: borrow more now to spend money on keeping people in work and in turn keep the deficit down.
In this case the money is coming from an expected windfall from the sale of the 4G mobile phone licenses. So Mr Balls does not need to find a equivalent cut to pay for his new spending plans.
But it's caused a row with the Conservatives about whether the Shadow Chancellor has done his sums.
Sources close to George Osborne say £600 million of the yet-to-be-received £3-4 billion has already been allocated.
They claim the Spending Review identified the money for the Department for Business for investment in science and further education.
Which begs the question, will Balls have less to spend or will he cut the money which the Conservatives claim has been allocated for "growth-boosting capital spending".
If Mr Balls' figures don't stack up, it won't do much for Labour's reputation for economic competence which is one of the principle aims of this conference.
Labour have now responded to the claims from the Treasury that the 4G money has already been allocated.
Ed Balls' office says the Chief Secretary to the Treasury, Danny Alexander, said this to MPs in the House of Commons in October 2011:
The Government made no assumptions at spending review 2010 about the level of receipts from the award of 800 MHz and 2.6 GHz spectrum [4G] licenses and no spending commitments are contingent upon these receipts.